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WO1999063293A1 - Systeme de regulation de temperature a echange thermique electrohydrodynamique - Google Patents

Systeme de regulation de temperature a echange thermique electrohydrodynamique Download PDF

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Publication number
WO1999063293A1
WO1999063293A1 PCT/US1999/012270 US9912270W WO9963293A1 WO 1999063293 A1 WO1999063293 A1 WO 1999063293A1 US 9912270 W US9912270 W US 9912270W WO 9963293 A1 WO9963293 A1 WO 9963293A1
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WO
WIPO (PCT)
Prior art keywords
fluid
electric field
applying
temperature
heat transfer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US1999/012270
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English (en)
Inventor
Chun Ho Lam
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Honeywell International Inc
Original Assignee
AlliedSignal Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by AlliedSignal Inc filed Critical AlliedSignal Inc
Publication of WO1999063293A1 publication Critical patent/WO1999063293A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F27/00—Control arrangements or safety devices specially adapted for heat-exchange or heat-transfer apparatus
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
    • F28F13/16—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by applying an electrostatic field to the body of the heat-exchange medium

Definitions

  • the present invention relates generally to heat exchange methods and apparatus and more especially to such methods and apparatus for controlling the rate of heat exchange between two media in a heat exchange device.
  • the temperature control system and techniques have aerospace, industrial, and commercial applications.
  • Conventional temperature control systems use a control valve to bypass a fluid around or to limit the flow through the heat exchanger to vary the heat transfer and achieve the temperature control objective, and usually have the following problems.
  • the system dynamics vary significantly. Maintaining control stability usually results in a less responsive system.
  • the valve is a nonlinear control device which adds to the control problems.
  • the valve being a mechanical device, is the most unreliable element.
  • the valve increases the total system weight and volume. It also increases the component installation and system development cost of the system. Since no heat transfer enhancement is applied, the heat exchanger is usually sized to cope with the worst operating conditions, resulting in added weight and volume penalties.
  • Figures 1 A and 1 B illustrate the prior approaches for controlling the fluid temperature
  • ⁇ is a time constant
  • NTU is the number of heat transfer units defined as the ratio of
  • T h0 indicates the controlled fluid temperature.
  • the desirable temperature is achieved by varying the flow W c , at temperature T ci , using the control valve S1.
  • the response speeds of valve S1 and the heat exchanger dominate the achievable dynamic response of T h0 - Since the response speed is a function of the time constant ⁇ of the component, a longer time constant implies that the response speed of the component is slower.
  • the heat exchanger time constant is a function of the heat transfer rates of both fluids and its thermal mass such that the time constant increases as the heat transfer rates decrease.
  • the heat exchanger response time at low flow conditions can be 10 times or longer than those at the high flow conditions.
  • the other effects are the changes in T o induced by changes in W c .
  • the ratio of change in T h0 and change in W c is known as the gain effect of the heat exchanger, and varies widely as a function of W c .
  • the smaller W c or Wh will also result in an appreciable increase in transit time ( time delay effects) of the fluid passing through the heat exchanger. All these effects have the tendency to degrade the resulting T h0 control system stability performance.
  • valve S1 Since valve S1 is a mechanical device, its performance will usually degrade as it ages, resulting in either valve failures or degradation in its hysteresis and backlash characteristics. These hysteresis and backlash effects will significantly degrade the control system stability. To anticipate the above performance degrading, the initial control system design is usually conservative to improve its robustness. This usually will result in a slow responding T h0 control system, which is undesirable for many temperature control applications.
  • the fluid heat transfer rates can be enhanced by applying an electric field to the fluid.
  • the degree of enhancement is a function of the field strength, which is proportional to the voltage applied to the fluid.
  • EHD electrohydrodynamic
  • the control voltage can be controlled with high accuracy and repeatability
  • the heat transfer rates can also be controlled with high accuracy and repeatability, eliminating the undesirable hysteresis and backlash effects commonly found in control valves.
  • the maximum time constant of the heat exchanger occurs when there is no heat transfer enhancement, it will always decrease as the heat transfer rate increases due to the EHD effects.
  • the fluid flow rates can remain constant for EHD type control operation, the constant time delay effects upon the control system dynamics can be more easily compensated for as compared to the valve type control systems.
  • U.S. Patent 4,651 ,806 there is disclosed a heat exchanger having a casing through which pass a plurality of spaced-apart tubes. Heat exchange takes place through the tube walls between a first fluid within the tubes and a second fluid outside them but within the casing. The rate of heat exchange is enhanced by electrohydrodynamic effect by means of an electrode comprising a sheet-form first part which encompasses the tubes, and connected second parts which run lengthwise through the spaces between the tubes. The first part may be mesh-like and the second parts may be mesh-like and/or rod-like. The electrode is excited to high voltage and the casing and tubes are grounded.
  • the effect of the second part is to make the electric field around the individual tubes more uniform than would be the case if the electrode consisted of the first part alone. It is desirable to utilize electrohydrodynamic heat transfer enhancement to provide temperature control in a compact, economical heat exchanger and to provide such control in a way to avoid the above noted problems.
  • the present invention provides solutions to the above by providing an improved method of controlling the time rate of heat transfer between two fluid media and includes sensing the temperature of one of the media and comparing that sensed temperature to a preferred temperature to determine the difference between the sensed and preferred temperatures. An electric field is then selectively applied, as a function of the sensed temperature error, to at least one and sometimes both of the liquid media to increase the time rate of heat transfer between the media whenever the comparison indicates differences between the sensed and preferred temperatures.
  • the electric field may be of a varying direct current and applied continuously, as a function of the sensed temperature error, or may be a variable pulse duration according to the difference between the sensed and preferred temperatures.
  • the maximum outlet temperature achievable is the inlet temperature Tm, and the minimum can approach T C j.
  • the maximum temperature control range is therefore the difference between Tw and T ci .
  • the temperature control range achievable for a given temperature control system is defined as the percentage of the maximum temperature control range.
  • ⁇ varies from 0 to a value approaching 1 .
  • the lowest ⁇ limit is achieved by using the valve S1 to cut off the flow to the heat exchanger.
  • the ⁇ high limit occurs when maximum W c is allowed to flow through the heat exchanger and the value is a function of the heat exchanger design.
  • the temperature control range achievable is usually less than those achievable by approaches 1 A and 1 B, because there is no valve to cut off the cold flow W c to the heat exchanger.
  • the lowest limit of ⁇ is greater than zero, implying that the maximum temperature attainable is less than the hot fluid inlet temperature Tm.
  • the achievable temperature control ranges also depend on the type of fluids used in the system. The temperature control range will be larger for applications using liquids or refrigerants than the gaseous applications, because the electrohydrodynamic enhancement effects on liquid and refrigerant type fluids are higher than those of gaseous type fluids.
  • FIG. 2 shows that the electrohydrodynamic temperature control approach is most effective when the heat exchanger is designed to operate at moderate NTU values and under the conditions that the cold side and hot side fluids have similar thermal capacities.
  • Ohadi, M.M., Nelson, D.A., Zia, S "Heat transfer enhancement of laminar and trubulent pipe flow via corona discharge”.
  • Ohadi, M.M. "Heat transfer enhancement in heat exchangers", ASHARE Journal, December 1991 , report that for PAO, oil, and refrigerant type fluids, the heat transfer enhancement effects can reach 15 times or higher, while that for air is about 3 times.
  • the temperature control range for the liquid to liquid type heat exchanger applications is in the order of 60% and that for the air to air applications is in the order of 25%.
  • the control range is in the order of 30%.
  • the present invention comprises in the transfer of heat between a fluid media and a second media, an improved method of controlling the time rate of heat transfer between the media comprising: sensing the temperature of one of the media; comparing the sensed temperature to a preferred temperature to determine the difference between the sensed and preferred temperatures; applying selectively an electric field to the fluid media to control the time rate of heat transfer between the two media as a function of the determined difference.
  • Figure 1A illustrates a prior temperature control method which utilizes flow limiting
  • Figure 1 B illustrates a prior temperature control method which utilizes flow bypass
  • Figure 2 illustrates typical trends of heat exchanger effectiveness ⁇
  • FIG 3 is a simplified cross-sectional view of a plate-fin type heat exchanger incorporating the invention
  • Figure 4 is a schematic representation of a temperature controlled heat exchange system according to the invention in one form
  • FIG. 5 is a schematic representation of the control function for the heat exchange system of Figure 3.
  • the present invention applies electric fields across the heat transfer fluids to enhance heat transfer within the heat exchanger.
  • the fluids are dielectric and the heat transfer is a function of the field strength. Consequently, temperature control can be achieved by changing the electric field magnitude, eliminating the control valve.
  • the approach should be most effective for liquid and working type fluids in terms of system size and weight impacts. For gas, the control concept is still applicable, but the weight and size impact will be less since the electrical field enhanced heat transfer effect is not as high as for either the fluid or refrigerant cases.
  • the system includes an electrohydrodynamic heat exchanger 1 1 with a set of electrodes 25, 29 and 25, 31 ( Figure 3) for each fluid passage, a temperature sensor 27, and one temperature controller 33 ( Figure 4) with two independent controllable high voltage supplies 35, 37 ( Figure 5) connected to the respective sets of electrodes.
  • the controllable heat exchange device has two chambers illustrated in Figure 3, but will typically have several adjacent chambers having opposed directions of fluid flow in each adjacent pair.
  • Chamber 13 has a fluid inlet 17 and a fluid outlet 21 while chamber 15 has inlet 19 and outlet 23 to give this opposing direction of flow effect as illustrated by the arrows within the chambers.
  • a heat conducting separator 25 functions as a common electrode and to separate one chamber from the other.
  • An electrode 29 is disposed in chamber 13 and electrically isolated from the common electrode 25.
  • the voltage V1 from power supply 37 ( Figure 5) is applied between electrodes 29 and 25.
  • electrode 31 is disposed in chamber 15 and voltage V2 from power supply 35 is applied between it and common electrode 25.
  • Pumps convey their respective fluids to the corresponding inlets so as to cause the fluids to flow near the surfaces of the separator 25.
  • the temperature of the first fluid is sensed by sensor 27 after it passes from the first chamber outlet 21.
  • power supplies 35 and 37 apply selectively electric fields to one or both of the fluids to control the rate of heat transfer there between.
  • both fluids are liquids and the fluid to which the electric field is applied is a dielectric fluid.
  • the temperature control error signal e r ( Figure 5) will be compensated for control performance and stability by K(s) which provides two output signals to drive the high voltage power supplies 35 and 37.
  • VI electrohydrodynamic
  • V2 electrohydrodynamic
  • That effectiveness threshold will vary with materials and dimensions, and may range from a few kilovolts up to more than 10 kilovolts. If Tp fails to reach the desirable set point after V2 reaches its maximum value, then VI will be allowed to vary to control Tp.
  • both VI and V2 will be allowed to rise and fall simultaneously at the same rate as required by K(s).
  • a variable DC voltage is used to excite the fluid.
  • the second approach is to use a pulse width modulation (PWM) scheme.
  • PWM pulse width modulation
  • the voltage will be at its maximum value when applied to the fluid.
  • the PWM duty cycle duration of the applied voltage will be a function of the control signal from K(s).
  • the PWM frequency should be higher than the control system bandwidth or such that the induced fluid turbulence onset and turn-off can follow the PWM turn-on and turn-off actions.
  • the present invention has the following advantages.
  • the system does not require a control valve normally used for bypassing or restricting the coolant flow to achieve temperature control. With fewer mechanical components, the system reliability will be higher, resulting in lower mechanical component and installation costs.
  • the system can achieve better control stability by eliminating the valve servo hysteresis, backlash, nonlinear valve area, and aging effects. Fluid flow rates through the heat exchanger will remain constant. This reduces the time constant variations and time delay effects of the dynamic system due to the flow bypassing or restricting effects, resulting in a potentially more stable control system. Finally, this approach may reduce the weight and volume for certain types of the heat exchanger.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Control Of Temperature (AREA)

Abstract

L'invention concerne un système de régulation de température amélioré à échange thermique hydrodynamique. En appliquant un champ électrique à un fluide caloporteur, il est possible de contrôler le coefficient de transfert de chaleur en fonction de la tension appliquée. Cette caractéristique permet de contrôler la quantité d'énergie calorifique échangée entre fluides. En contrôlant ce transfert, on peut contrôler la température d'évacuation du fluide considéré. Un dispositif d'échange thermique (11) peut comprendre deux chambres (13, 15) équipées chacune d'une admission de fluide (17, 19) et d'une sortie de fluide (21, 23). Une barrière constituant une isolation par rapport au fluide, assurant une conduction thermique et tenant lieu d'électrode commune (25) sépare les chambres. L'introduction de fluide dans les chambres s'effectue selon des directions généralement opposées, afin que les fluides s'écoulent dans des directions opposées à proximité de la surface de la barrière (25). La température d'un fluide est détectée par un capteur de température (27) après le passage de ce fluide par une sortie (21), et le champ électrique est appliqué au moins à l'un des fluides, ce qui a pour effet d'améliorer le degré de transfert thermique entre les deux fluides et de conférer la température recherchée au fluide considéré.
PCT/US1999/012270 1998-06-02 1999-06-02 Systeme de regulation de temperature a echange thermique electrohydrodynamique Ceased WO1999063293A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US8900598A 1998-06-02 1998-06-02
US09/089,005 1998-06-02

Publications (1)

Publication Number Publication Date
WO1999063293A1 true WO1999063293A1 (fr) 1999-12-09

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6932580B2 (en) 2000-07-18 2005-08-23 Illinois Institute Of Technology Electrohydrodynamic conduction pump
US7334627B2 (en) * 2002-12-12 2008-02-26 Industrial Technology Research Institute Enhanced heat transfer device with electrodes
CN108466485A (zh) * 2018-03-21 2018-08-31 嘉兴学院 近场电流体动力喷印工作电压具有短延迟时间的控制方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3763928A (en) * 1972-06-28 1973-10-09 Nasa Electrostatically controlled heat shutter
EP0177211A2 (fr) * 1984-09-24 1986-04-09 National Research Development Corporation Echangeurs de chaleur
US4890667A (en) * 1988-10-17 1990-01-02 Battelle Memorial Institute Method and apparatus for improving heat transfer in a fluidized bed
DE29505723U1 (de) * 1995-04-03 1996-08-01 Viehmann, Matthias, Dipl.-Ing., 06526 Sangerhausen Intelligenter Wärmeleiter

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3763928A (en) * 1972-06-28 1973-10-09 Nasa Electrostatically controlled heat shutter
EP0177211A2 (fr) * 1984-09-24 1986-04-09 National Research Development Corporation Echangeurs de chaleur
US4651806A (en) 1984-09-24 1987-03-24 National Research Development Corporation Heat exchanger with electrohydrodynamic effect
US4890667A (en) * 1988-10-17 1990-01-02 Battelle Memorial Institute Method and apparatus for improving heat transfer in a fluidized bed
DE29505723U1 (de) * 1995-04-03 1996-08-01 Viehmann, Matthias, Dipl.-Ing., 06526 Sangerhausen Intelligenter Wärmeleiter

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
OHADI, M.M. ET AL.: "HEAT TRANSFER ENHANCEMENT OF LAMINAR AND TRUBULENT PIPE FLOW VIA CORONA DISCHARGE", INT. J. HEAT MASS TRANSFER, vol. 34, no. 4..5, 1991, pages 1175 - 1187
OHADI, M.M.: "HEAT TRANSFER ENHANCEMENT IN HEAT EXCHANGERS", ASHARE JOURNAL, December 1991 (1991-12-01)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6932580B2 (en) 2000-07-18 2005-08-23 Illinois Institute Of Technology Electrohydrodynamic conduction pump
US7334627B2 (en) * 2002-12-12 2008-02-26 Industrial Technology Research Institute Enhanced heat transfer device with electrodes
CN108466485A (zh) * 2018-03-21 2018-08-31 嘉兴学院 近场电流体动力喷印工作电压具有短延迟时间的控制方法
CN108466485B (zh) * 2018-03-21 2019-05-17 嘉兴学院 近场电流体动力喷印工作电压具有短延迟时间的控制方法

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